Radio repeater trunking (time sharing of a single repeater communications channel among many users) is well-known. Early trunking systems used analog control signals while some more recent systems have utilized digital control signals. Control signals have been utilized on a dedicated control channel and/or on different ones of the working channels for various different reasons and effects. A non-exhaustive but somewhat representative sampling of publications and patents describing typical prior art trunked radio repeater systems is identified below:
U.S. Pat. No. 3,898,390, Wells et al (1975) PA0 U.S. Pat. No. 4,392,242, Kai (1983) PA0 U.S. Pat. No. 4,534,061, Ulug (1985) PA0 U.S. Pat. No. 4,649,567, Childress (1987) PA0 U.S. Pat. No. 4,658,435, Childress et al (1987) PA0 U.S. Pat. No. 4,716,407, Borras et al (1987) PA0 JAPAN 61-102836 (A) Ishikawa (May 1986) PA0 U.S. Pat. No. 3,292,178, Magnuski (1966) PA0 U S. Pat. No. 3,458,664, Adlhoch et al (1969) PA0 U.S. Pat. No. 3,571,519, Tsimbidis (1971) PA0 U.S. Pat. No. 3,696,210, Peterson et al (1972) PA0 U.S. Pat. No. 3,906,166, Cooper et al (1975) PA0 U.S. Pat. No. 3,936,616, DiGianfilippo (1976) PA0 U.S. Pat. No. 3,970,801, Ross et al (1976) PA0 U.S. Pat. No. 4,001,693, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,010,327, Kobrinetz et al (1977) PA0 U.S. Pat. No. 4,012,597, Lynk, Jr. et al (1977) PA0 U.S. Pat. No. 4,022,973, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,027,243, Stackhouse et al (1977) PA0 U.S. Pat. No. 4,029,901, Campbell (1977) PA0 U.S. Pat. No. 4,128,740, Graziano (1978) PA0 U.S. Pat. No. 4,131,849, Freeburg et al (1978) PA0 U.S. Pat. No. 4,184,118, Cannalte et al (1980) PA0 U.S. Pat. No. 4,231,114, Dolikian (1980) PA0 U.S. Pat. No. 4,309,772, Kloker et al (1982) PA0 U.S. Pat. No. 4,312,070, Coombes et al (1982) PA0 U.S. Pat. No. 4,312,074, Pautler et al (1982) PA0 U.S. Pat. No. 4,326,264, Cohen et al (1982) PA0 U.S. Pat. No. 4,339,823, Predina et al (1982) PA0 U.S. Pat. No. 4,347,625, Williams (1982) PA0 U.S. Pat. No. 4,360,927, Bowen et al (1982) PA0 U.S. Pat. No. 4,400,585, Kamen et al (1982) PA0 U.S. Pat. No. 4,409,687, Berti et al (1983) PA0 U.S. Pat. No. 4,430,742, Milleker et al (1984) PA0 U.S. Pat. No. 4,430,755, Nadir et al (1984) PA0 U.S. Pat. No. 4,433,256, Dolikian (1984) PA0 U.S. Pat. No. 4,450,573, Noble (1984) PA0 U.S. Pat. No. 4,485,486, Webb et al (1984) PA0 U.S. Pat. No. 4,578,815, Persinotti (1985) PA0 channel A to police squad A, PA0 channel B to police squad B, PA0 channel C to rescue squad/paramedics, PA0 channel D to snow removal equipment, PA0 channel E to municipal vehicles, PA0 channel F to fire squad A, and PA0 channel G to fire squad B. PA0 U.S. Pat. No. 4,594,591 to Burke PA0 U.S. Pat. No. 4,517,561 to Burke et al PA0 U.S. Pat. No. 4,152,647 to Gladden et al PA0 U.S. Pat. No. 4,612,415 to Zdunek et al PA0 U.S. Pat. No. 4,427,980 to Fennel et al PA0 U.S. Pat. No. 4,553,262 to Coe PA0 U.S. Pat. No. 4,457,018 to Takayama (1984) PA0 U.S. Pat. No. 4,573,206 to Grauel et al (1986) PA0 U.S. Pat. No. 4,573,209 to Deman et al (1986) PA0 U.S. Pat. No. 4,644,347 to Lucas et al (1987) PA0 U.S. Pat. No. 4,677,653 to Weiner et al (1987) PA0 U.S. Pat. No. 4,734,928 to Weiner et al (1988)
There are many actual and potential applications for trunked radio repeater systems. However, one of the more important applications is for public service trunked (PST) systems. For example, one metropolitan area may advantageously use a single system of trunked radio repeaters to provide efficient radio communications between individual radio units within many different agencies. As is well-known to those familiar with trunking theory, a relatively small number of radio repeaters can efficiently service all of needs of a public service organization within a given geographic area if they are trunked (i.e., shared on an "as-needed" basis between all potential units).
Before modern trunked radio repeater systems were developed, mobile radio transceivers were provided with crystal controlled frequency synthesizers providing a limited number of fixed transmit/receive channels--and the various channels were assigned for use by different "groups" of radio transceivers. Referring to FIG. 1, for example, fixed channels might be assigned as follows:
Every mobile transceiver in a group was capable of communicating with other members of its group (and with a central dispatcher) over its assigned communications channel.
This type of arrangement, although certainly providing private and reliable communications, had some severe disadvantages. One important disadvantage was that some channels were under-utilized while other channels were extremely congested (e.g., during disasters or emergencies requiring coordination between many different users). Moreover, the number of required communications channels and associated RF repeaters was directly proportional to the number of groups supported by the system. As RF channels became more scarce, it was no longer practical in major metropolitan areas to dedicate RF frequencies to only a single group of users and some method of sharing frequencies between multiple user groups was required.
Trunked radio repeater systems rely upon software controlled transceiver frequency control rather than crystal controlled preset operating frequencies. Generally, a certain number of RF communications channels (e.g., 12 or 24 channels per repeater site) are allocated (by governmental authorities) to a communications system. The communications system provides a radio repeater for each of these RF channels, and temporarily assigns these channels on an "as needed" basis for exclusive use by calling mobile units requesting communications and the group(s) of mobile units being called.
This trunked arrangement provides for much additional flexibility. Even though all of these groups are in effect "reusing" the same communications channels in this trunked radio system, the trunking is mostly transparent to individual users. For example, when a police officer in police squad A switches his "channel" (actually group) selector switch to correspond to the first group and actuates his "push-to-talk" microphone switch to make a call, his transceiver and all other active transceivers of police squad A are automatically controlled to switch to a free "working" channel temporarily dedicated to their use--and significantly, no other mobile transceivers are permitted to monitor or participate in the communications over this channel. This privacy feature afforded by trunked communications systems is important for providing each group of users with efficient, reliable communications. Thus, in this respect the trunked system behaves from a user's view point like the prior systems in which each service had a channel dedicated to its exclusive use--while providing the resource (radio spectrum and repeater equipment) economy derived from channel and repeater sharing.
Mobile and portable transceivers are typically preprogrammed in advance at the time of sale by the manufacturer (or equipment distributor) for the specific set of RF frequencies (and other "personality" information) used by a particular system. This programming is typically accomplished by connecting the transceiver to a dedicated programming device and loading a frequency allocation table (and other information) into an internal non-volatile "personality PROM" memory device within the transceiver. See commonly assigned U.S. Pat. No. 4,525,865 to Mears (1985) and copending commonly assigned application Ser. No. 06/910,353 now U.S. Pat. No. 4,843,588 of Flynn et al filed Sept. 22, 1986 for two examples of how this programming may be accomplished.
One of the disadvantages of most prior art transceiver "personality" programming techniques is that they require a hard-wired connection between the transceiver to be programmed and a programming device--and thus require the transceiver to be taken out of service and brought from the field into a central location (e.g., a distributor's repair shop or service depot) for reprogramming. While this type of programming operation is quite practical as part of the testing procedure involved in placing new transceivers into service, it is generally not practical to physically recall hundreds or thousands of transceivers already in service for a particular trunked communications system into a service depot in order to reprogram them to accommodate new system capabilities or the like.
Of course, system designers take great pains to ensure that all improvements, enhancements and additional features added to the system are compatible with existing, earlier versions of transceivers already in the field. Just as black and white television receivers are capable of receiving color television transmissions and displaying those color images in the black and white format, older mobile transceivers must remain fully capable of providing all of the functions they were designed to provide--even when the overall system is "upgraded" to provide additional, more advanced functions. This makes it possible to install new transceivers capable of taking advantage of such upgraded functions without requiring the older transceivers to be overhauled. As is well known, one way to ensure such "upward compatibility" exists is to make the program controlled steps performed by the transceivers themselves as simple and non-limiting as possible, so that system enhancements made by changing the site controller programming can be fully participated in by even the older mobile transceivers. However, there are certain functions the mobile transceivers must perform independently, and these functions cannot generally be changed except by reprogramming each and every mobile transceiver.
One of the functions the mobile transceiver must perform on its own is to scan all possible active frequencies on a system. At the time a transceiver is first turned on, one of the first things it typically does is to "listen" in sequence on each of the RF channels stored in non-volatile form in its internal frequency allocation table to locate an active digital control channel. Once the control channel is found, the transceiver monitors the channel for call messages. A call message may direct the transceiver to retune to a working channel, but such call messages typically do not explicitly specify the transmit and receive frequencies of the working channel but instead require the transceiver to once again reference its internally stored frequency allocation table to obtain the information its frequency synthesizer requires to retune to the designated working channel.
FIG. 2(A) schematically shows an exemplary configuration of a prior art trunked radio communications system 100 including a mobile transceiver 152 and ten trunked RF repeater stations 300(1)-300(10) operating on logical RF channels 1-10 respectively. Mobile transceiver 152 includes a "personality-defining" non-volatile memory device 152a which stores a frequency allocation table defining logical and physical channel numbers for all ten RF channels. This table is used to control a frequency synthesizer 152b, which in turn controls the transmit and receive frequencies of RF transmitter/receiver section 152c.
Due to the limited nature of frequency spectrum resources, governmental licensing authorities (e.g., the Federal Communications Commission in the United States) are generally very stingy about allocating RF frequencies to those who apply for them. For example, when a trunked radio repeater system is first constructed and installed, only a few RF channels may be allocated to the system. Generally, additional RF channels are granted only on an "actual need" basis after the system has matured and it can be shown that the additional channels are actually required to accommodate system traffic. While this policy of granting channels based on actual need prevents channels from being wasted, it causes a fundamental problem in prior art trunked communications systems architectures as is demonstrated by FIG. 2B.
Since additional channels are granted only to a mature repeater system, there will typically be hundreds of transceivers already in the field that are programmed to operate only on the system's initially allocated frequencies (i.e., the frequencies being used before new channels are allocated to the system). FIG. 2B shows one such exemplary transceiver 152 storing a frequency allocation table which does not define three additional channels 11-13 added to the system after the transceiver was installed. While it would be highly desirable to reprogram transceiver 152 (and all of the other transceivers installed prior to the addition of the new channels) with the new frequencies, reprogramming all existing transceivers is a huge task that is generally too costly and time consuming to be considered. Typically, transceivers placed into the field after the new channels have been allocated are programmed with the new channels, but all transceivers in use before the new allocation (e.g., transceiver 152 shown) continue to be capable of operating on only the initially allocated channels. Suppose a call is issued to transceiver 152 and to all other transceivers in its group to move to a new channel (e.g., channel 13) as a working channel. Transceiver 152 does not have an entry in its stored frequency allocation table corresponding to new logical channel 13, and is therefore incapable of retuning to this new channel. The result is that transceiver 152 is incapable of participating in a call intended for it, and the user issuing the call must try again (and hope one of the originally allocated channels will be free and assigned for use as the working channel).
One possible solution to this problem would be to keep track of which groups contain any transceivers put into the field before the new channels were installed and inhibit the new channels from being assigned as working channels for such groups. This situation, however, can lead to severe under-utilization of the new channels--at the same time that the initially allocated channels are being heavily loaded or over-loaded. Moreover, keeping track of which groups can operate on the new channels and which groups cannot is a rather time consuming task which wastes other system resources as well (e.g., site controller storage and processing time resources).
Needless to say, the inflexibility resulting from preprogrammed fixed frequency allocation tables stored in "personality PROMs" within individual radio transceivers arises in other situations as well (e.g., when transceivers from one system must be used with proper authorization on another system, when two existing mature systems are to be combined into a single system, and the like).
The concept of downloading information into radio transceivers via RF signals in a trunked radio system is generally known. For example, "dynamic regrouping" allows a system operator to program customized group identifications into radio transceivers in the field from the central system facility at will--and dynamically form special groups for special purposes. Motorola, Inc. of Shaumburg, Ill. has developed a so-called "SMARTNET" trunked radio communications system which offers a limited dynamic regrouping capability. The optional dynamic regrouping capability provided in this 800 MHz trunked system allows the dispatcher to reassign radios into new talk groups without any mobile operator involvement to provide communications flexibility during emergency situations. Motorola's subscriber dynamic regrouping communications system is described in WO PCT Patent Publication No. 8701537 published 12 March 1987 entitled "Method For Dynamically Regrouping Subscribers On A Communications System", and in press releases dated Aug. 6, 1987 and June 27, 1986.
Briefly, the Motorola scheme provides for downloading a single dynamic reprogramming instruction to specified individual radio transceivers in the field via digital messages transmitted over the RF control channel to each of the transceivers individually. Upon receipt of the reprogramming message, the individual transceivers acknowledge the message, store the downloaded dynamic regroup identifier in an internal memory, and switch to a dynamic regroup mode in which they transmit and receive using the dynamic group instead of their old group(s). In another mode, a "group" dynamic regroup message is transmitted to an entire group of transceivers at a time in order to increase regrouping speed. The receiving transceivers begin using an alternate, fixed "dynamic code" previously programmed at time of manufacture and/or "personality PROM" programming. The units continue to use this "dynamic code" until dynamic regrouping messages cease being periodically transmitted over the control channel.
The following issued U.S. Patents may also be generally relevant to the concept of dynamically reprogramming radio transceivers via over-the-air control messages:
In addition, AmeriCom Corporation of Atlanta, Ga. has advertised an RF communications system featuring "over the air reprogramming to add channels and reprogram mobiles without expensive PROM changes." AmeriCom claims a "customer radio data base management feature" which provides "more responsive service by dynamically reprogramming mobiles from the terminal" in order to lower service costs and permits real time "over-the-air reprogramming of radio configurations and permissions." These features are described in various advertisements and specifications published by AmeriCom, including various product profile brochures dated Jan. 26, 1988 entitled "AmeriCom's Network Switch" and "AmeriCom's Network Supervisor."
Commonly assigned copending application Ser. No. 07/229,814 Childress et al filed Aug. 8, 1988 entitled "Dynamic Regrouping In A Trunked Radio Communications System" describes a technique for dynamically regrouping transceivers via RF messages.
The following additional prior issued U.S. patents may also be generally relevant:
The Lucas '347 patent discloses an arrangement in which commands transmitted to a pager cause it to alternately monitor different preprogrammed local channels--thereby permitting the pager to be used in different cities. The Grauel '206 patent discloses an ability to dynamically change the number of transceivers monitoring different control channels in a multiple control channel system.
The present invention provides an improved trunked RF communications arrangement which dynamically "expands" or extends the frequency allocation table stored within the "personality" defining non-volatile storage devices of all transceivers to include additional RF channels. In the preferred embodiment, a special channel configuration control message is periodically transmitted over the active RF control channel. This channel configuration message specifies a logical channel field and an FCC channel number which exactly defines the RF frequency of the logical channel being dynamically allocated. All transceivers which correctly receive this channel configuration message extend their stored frequency allocation tables to add the additional channel entry specified by the message. FIG. 3 shows an exemplary system configuration in which a transceiver 152 has received three such channel configuration messages corresponding to three additional channels 11-13 and has added three corresponding new records to its stored frequency allocation table. The transceiver 152 references these additional records in response to call messages specifying new channels, and is thus capable of operating on the new channels.
In accordance with yet another feature of the present invention, no acknowledgements from individual transceivers are sent or required for dynamic reprogramming. Instead, all channel configuration messages are periodically repeated at relatively short intervals (e.g., a channel configuration message is transmitted every ten seconds, with the frequency of retransmission of a given channel configuration message depending upon the number of channels supported by the communications system in the preferred embodiment). The intervals are long enough to ensure the messages have no real adverse impact on control channel loading, but short enough to ensure that any transceiver which receives and stores incorrect information or has "older" programming will soon correct/update its frequency allocation table by overwriting it with correct information.
In addition, errors are prevented from occurring by transmitting the channel configuration message in both slots of an outbound control channel message, so that the mobile transceivers receive two (supposedly identical) messages virtually simultaneously. Any mobile transceiver which receives different channel configuration message data in the same two-slot message assumes one or both versions of the received message are erroneous and ignores both versions of the message. Transceivers are further prevented from adding invalid channels to their frequency allocation tables by requiring receipt of a non-zero site identification control message before processing any channel configuration message.